Astronomers see unusually bright supernovae from early universe

Australian astronomers using a Hawaiian telescope have observed two so-called super-luminous supernovae, only the second and third such objects ever discovered. The new supernovae, 10 to 100 times brighter than conventional supernovas, are from the earliest stages of the universe and are thought to occur by a different mechanism, the researchers reported online Friday in the journal Nature.

Conventional supernovae shine extremely brightly for several weeks or months, putting out more light than the entire galaxies they reside in. They typically have two causes: either the re-ignition of nuclear fusion in a degenerate star or the collapse of the core of a massive aging star. Alternatively, a white dwarf star may accumulate sufficient mass from a nearby companion to trigger carbon fusion and an explosion.

Super-luminous supernovae arise from the death of extremely massive stars, such as those that were formed in the first 2 billion to 3 billion years after the big bang. Such stars could be more than 100 times as massive as the Earth's sun. The super-luminous supernovae occur when a nuclear explosion is triggered by the conversion of photons into electron-positron pairs, which can occur when photons of visible light collide with gamma-rays.

A team headed by astronomer Jeff Cooke of Swinburne University of Technology in Hawthorn, Australia, used the Low Resolution Imaging Spectrometer on the 10-meter (394-inch) Keck Telescope on Mauna Kea to search for super-luminous supernovae at extreme distances from Earth -- that is, in the earliest stages of the universe. The discovery suggests that the super-luminous supernovae were at least 10 times more common in the early universe than they are among nearby galaxies.

"Detecting the supernovas allows us much greater understanding of the first stars in the universe," Cooke said. "Shortly after the big bang, there was only hydrogen and helium in the universe. All the other elements that we see around us today, such as carbon, oxygen, iron and silicon, were manufactured in the cores of stars or during supernova explosions. The first stars to form after the big bang laid the framework for the long process of enriching the universe that eventually produced the diverse set of galaxies, stars and planets we see around us today."